Leuco dye type heat-sensitive recording materials are normally employed as the recording material used in a heat-sensitive recording method. However, these heat-sensitive recording materials have a disadvantage in that unexpected coloration arises as a result of rough handling, heating or contact with solvents after a recording has been made, and the recorded image is inevitably stained. Active research has been carried out in connection with diazo based heat-sensitive recording materials in recent years as heat-sensitive recording materials which are not prone to disadvantages of this sort. For example, JP-A-No. 57-123086 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-No. 58-160190, JP-A-No. 57-169390 and JP-A-No. 59-2887, and the Journal of the Electric Imaqe Society, 11, 290 (1982) etc., have disclosed the performance of thermal recording by using materials comprising a diazo compound, a coupling component and a basic component (including substances which become basic on heating). These disclosures indicate that after thermal recording is performed, the unreacted diazo compound is degraded by irradiation with light to prevent further color formation. Thus, it is possible in this way to stop color formation in the portions of the material where recording is not required (this stoppage is referred to below as "fixation").
Furthermore, JP-A-No. 59-190886 has disclosed heat-sensitive recording materials comprising microcapsules in which at least one component which takes part in the color forming reaction is included as a core material. The walls of these microcapsules are formed around this core material by polymerization in order to prevent the occurrence of pre-coupling during storage.
However, in recent years, as the range of applications for heat-sensitive recording materials has become more widespread, it has become essential to maintain a high quality recorded image over long periods of time. Even with the aforementioned diazo type heat-sensitive recording materials, it is desired that better color forming properties should be provided, that the storage stability should be improved and that the light resistance of the recorded image should be improved. It is therefore desirable that coloration of background after fixation should be slight even when fixable materials are used.